Rotary drive apparatus for selectively driving a tool at high torque, low speed and low torque, high speed that is used in making up and breaking out rod joints of, for example, a drill stem.
In the prior art, for example see U.S. Pat. No. 3,625,095 to Barnett et al, it is old to provide power driven pipe tongs for making up and breaking out joints of a drill stem and which are capable of spinning a pipe at high speed, low torque and at low speed, high torque. The Barnett apparatus includes a piston cylinder combination and hydraulic motors to provide the sources of power. However, the construction thereof is relatively complex.
U.S. Pat. No. 3,518,903 to Ham et al discloses a power tong assembly and a dependingly mounted backup tong assembly, the power tong assembly being powered by a hydraulic motor and the backup assembly by a piston cylinder combination. In U.S. Pat. No. 2,019,814 to Holmes et al there is disclosed a chuck having a gear toothed ring intermeshing with a rack that is reciprocated by a piston cylinder combination.
In order to provide a single unit of relatively simple construction that has a constant horsepower producing multitorque and multi-speed output, this invention has been made.